1. Field of the Invention
The present invention relates to an image recognition apparatus and method suited to an image capturing apparatus such as a video camera.
2. Description of the Related Art
There has been recently proposed an image capturing apparatus having an object recognition function of recognizing a specific object contained in an image. With the object recognition function, the image capturing apparatus can control the focus and exposure preferentially for a recognized object. The image capturing apparatus having the object recognition function first detects an object image region containing a specific object from image data obtained by object recognition processing by the image capturing apparatus. Then, the image capturing apparatus extracts feature information from the image data of the detected object image region to identify the object region as a recognition target. The image capturing apparatus compares the extracted feature information with that of an image registered in advance in a database. Based on the similarity obtained by the comparison, the image capturing apparatus recognizes a registered target which corresponds to the recognition target, or determines whether no corresponding registered target exists.
For example, Japanese Patent Laid-Open No. 2003-187352 proposes a system which performs personal recognition to detect a person's face as a specific object region, extracts feature information of the face, and determines the person having this face. In this specification, processing of identifying the person (object) corresponding to a detected image such as a face will be called “recognition”.
As described above, in object recognition, the similarity is calculated by comparing a recognition target with a target registered in advance in a database. A predetermined threshold is set for similarity to be calculated. If the calculated similarity is equal to or higher than the predetermined threshold, it is determined that the recognition target coincides with a target in the registration database.
When feature amounts obtained from the image of the recognition target and the image of the target in the registration database are almost equal, the similarity is high. However, even when the recognition target and the target registered in the database represent the same object, if the object status such as the object direction or brightness has changed, feature amounts (i.e. characteristics of the object and target that are compared) obtained from the target images differ from each other, and the similarity becomes low. The similarity becomes lower than the predetermined threshold because (1) the recognition target does not coincide with a target registered in the database, or (2) the status of a target registered in the database does not coincide with that of an object serving as the recognition target. That is, it cannot be determined from only the similarity value that the recognition target is an object not registered in the database.